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A new study by the Insurance Institute for Highway Safety (IIHS) found fresh evidence that cameras at intersections stop some drivers from running red lights.

Researchers studied the impact of red-light cameras at four major intersections in Arlington, Va. One year after ticketing began for red-light runners caught on camera, violations dropped 86 percent for the most dangerous instances, those occurring 1.5 seconds or longer after the light turned red. Violations happening at least 1 second after the light turned red dropped 48 percent, and those occurring at least one-half second after the light changed dropped 39 percent.

"What these numbers show is that those violations most likely to lead to a crash are reduced the most," Anne McCartt, senior vice president for research at IIHS and the study's lead author, said in a press statement. "The longer the light has been red when a violator enters an intersection, the more likely the driver is to encounter a vehicle traveling in another direction or a pedestrian."

The study builds on previous research. A 2011 IIHS study of large cities with longstanding red-light cameras found that the cameras reduced the fatal crash rate for red-light violations by 24 percent and the rate of all types of fatal crashes at intersections with traffic signals by 17 percent

The study videotaped traffic at the intersections before the cameras were installed and during three periods after the cameras were turned on. Researchers also looked at whether the red-light cameras had any spillover effect on nearby intersections. They found that results were smaller and not always statistically significant at two non-camera intersections in the same corridor. At two other non-camera sites located off the corridor, the odds of violations increased.

The lack of a broad spillover effect isn't surprising, McCartt said.

"Given the small number of cameras and signs, it's likely that many Arlington drivers didn't even know about the enforcement, while those who were aware probably knew the cameras were limited to a few locations," she said in a press release.

In the study, each of the four intersections got one camera covering a single approach. Following a 30-day warning period, the county began issuing citations carrying $50 fines for violations caught on camera. A press release was issued when the cameras were turned on and then another when ticketing began. Signs were installed at the camera-enforced approaches, but nowhere else.